An underage female who consumes excessive amounts of alcohol on most days of the week with no regard to school, friends, or family.

Chronic drunkenness is a key factor along with, but not limited to, losing car keys in dangerous areas, out of control slutty behavior, laying in the middle of the street, and being picked up by police.
It is also indicative of a "sloptart" to falsely accuse herself of being hammered drunk in order to have intercourse with a total stranger. This not only makes her feel better about herself, but tricks others into thinking she is making a drunken mistake.

Feel free to add adjectives in front of "sloptart" to better personalize the term.

Danielle is laying in the street again after screwing that random guy.... What a sloptart...

"Hey bro! I was thinking of hooking up with this chick. What you think?"

This is not a girl you take out on a date, sleep with or even show remote interest in. She simply exists so you and your friends can ridicule her endlessly til she decides to find her dignity and change her repulsive ways.

Man 1: You see that girl over there?

Man 2: Yeah, what about her?

Man 1: She used to be hot, but after I dumped her she turned into a total slop tart.